1. Field of the Invention
The present invention relates generally to a mobile communication system, and more particularly, to a method and apparatus for transmitting a Session Initiation Protocol (SIP) message by a User Equipment (UE) in an idle mode (hereinafter referred to as an “idle mode UE”) in an Internet Protocol Multimedia Subsystem (IMS) system.
2. Description of the Related Art
FIG. 1 is a diagram illustrating control plane architecture of a 3rd Generation Partnership Project (3GPP) system.
Referring to FIG. 1, reference numeral 101 denotes a protocol stack of a UE, reference numeral 111 denotes a protocol stack of a Radio Access Network (RAN), and reference numeral 121 denotes a protocol stack of a Core Network (CN).
The RAN 111, a network for managing radio access, is composed of Node B(s) and Radio Network Controller(s) (RNC). The Node B is a radio communication apparatus that directly participates in communication with the UE 101, and one Node B manages a plurality of cells. The RNC controls a plurality of Node Bs, and controls radio resources.
An interface between the UE 101 and the RAN 111 is called a Uu interface. The Uu interface and a Radio Resource Control (RRC) layer transmit/receive control information related to a radio access between the UE 101 and the RAN 111. In an upper node, the RRC layer is located in the RNC.
Control information of a lower node of the RRC layer will herein be referred to as Access Stratum (AS) control information.
An interface between the RAN 111 and the CN 121 is called an Iu interface. The Uu interface, the Iu interface, and a Call Control (CC)/Mobility Management (MM)/Session Management (SM)/Packet Mobility Management (PMM) layer transmit/receive control information related to call, session and/or mobility between the UE 101 and the CN 121.
The CC layer controls a Circuit Service (CS) call of the UE 101, exchanges service context information with the UE 101 for the CS call, and manages the information. The MM layer monitors and manages mobility of the UE 101 for the CS call.
The SM layer controls a session for a Packet Service (PS) of the UE 101, exchanges service context information with the UE 101 for the PS, and manages the information. The PMM layer monitors and manages mobility of the UE 101 for the PS service.
The CC/MM layer is located in a Mobile Switch Center (MSC), and the SM/PMM layer is located in a Serving GPRS Support Node (SGSN).
Control information of the CC/MM/SM/PMM layer in an upper node of the RRC layer will herein be referred to as NonAccess Stratum (NAS) control information.
Functions of the Node B, RNC, SGSN and MSC in FIG. 1 follow the 3GPP standard. In addition, Radio Link Control (RLC), Multiple Access Control (MAC), and Physical (PHY) layers are not directly related to the present invention. Functions of the other non-described layers follow the 3GPP standard.
FIG. 2 is a diagram illustrating a procedure for transmitting an SIP message for an IMS service by an idle mode UE in a 3GPP system.
Generally, in the 3GPP system, for efficient power use, an idle mode UE receives a Paging Indicator Channel (PICH) for determining the presence/absence of paging using a Discontinuous Reception (DRX) length, if there is no service or data being received.
In other words, the idle mode UE has no signaling connection for transmission/reception of control information between network nodes and also has no data channel for data transmission/reception, and service context information for the idle mode UE exists only in the MSC or SGSN, and does not exist in the RNC.
A description is provided of control information for the PS service and network nodes for the PS service. For example, in FIG. 1, control information of the SM/PMM layer in the NAS control information corresponds to the control information for the PS service. That is, the service context for the idle mode UE is managed by the SGSN.
Referring to FIG. 2, reference numeral 201 denotes a UE capable of receiving an IMS service, reference numeral 202 denotes a Node B for controlling a cell where the UE 201 is located, reference numeral 203 denotes an RNC for controlling the Node B 202, and reference numeral 204 denotes an SGSN to which the RNC 203 belongs.
If the UE 201 is in an idle mode and needs to transmit SIP data for the IMS service by an upper layer, the UE 201 should transition from the idle mode to a connected mode.
In step 211, the idle mode UE 201 performs an RRC connection establishment procedure.
In the idle mode UE 201, SIP data that needs to be transmitted by the upper layer can be transmitted through an INVITE message (hereinafter simply referred to as “INVITE”) and a PERIODIC REGISTER message. The SIP protocol is a protocol for initializing a session between a destination UE and a source UE for IMS service reception, and the INVITE is SIP protocol data transmitted to open the IMS service session in order to send an IMS service request to a destination UE and adjust Quality of Service (QoS) of the service session.
In the RRC Connection Establishment of step 211, signaling connection between the UE 201 and the RNC 203 is established. Step 211 includes a messaging procedure of an RRC CONNECTION REQUEST message transmitted from the UE 201 to the RNC 203, an RRC CONNECTION SETUP message transmitted from the RNC 203 to the UE 201, and an RRC CONNECTION SETUP COMPLETE message transmitted from the UE 201 to the RNC 203.
Therefore, due to the RRC connection setup, the UE 201 and the RNC 203 form a channel on a radio interface, capable of transmitting AS control information and NAS control information. Control information included in the RRC connection establishment procedure is the AS control information.
After the RRC connection of step 211 is established, the UE 201 transmits a SERVICE REQUEST message in step 221.
The SERVICE REQUEST message establishes a logical association between the UE 201 and the SGSN 204, and NAS control information between the SGSN 204 and the UE 201 can be transmitted/received through the logical connection. That is, a path on the Uu interface for transmission of control information between the UE 201 and the RNC 203 is established through the RRC connection establishment, and a path on the Iu interface for transmission of control information between the RNC 203 and the SGSN 204 for the UE 201 is established through the SERVICE REQUEST message. In addition, the SERVICE REQUEST message includes service type information and Packet Data Protocol (PDP) Context status information.
Therefore, using service type information of the service desired by the UE 201 and PDP context information kept in the SGSN 204, the RNC 203 and the SGSN 204 can set up a Radio Access Bearer (RAB) for transmission of the service data.
The RAB setup process starts with a RAB ASSIGNMENT REQUEST message of step 241. Iub data transport bearer setup is provided from the Node B 202 to the RNC 203 in step 242. A RADIO BEARER SETUP message is sent from the RNC 203 to the UE 201 in step 243, and a RADIO BEARER COMPLETE message is sent from the UE 201 to the RNC 203 in step 244. The RAB setup is completed when the SGSN 204 receives a RAB ASSIGNMENT RESPONSE message of step 245.
That is, in order to transmit SIP data, the UE 201 sends a service request message to the SGSN 204. Upon receipt of the service request message, the SGSN 204 sets up a RAB for SIP data transmission, and then can transmit the SIP data through the set SIP RAB.
Steps 231 through 234 correspond to a procedure for local authentication between the UE 201 and the RNC 203.
In step 231, the RNC 203 receives, from the SGSN 204, a Ciphering key (Ck) and an Integrity check key (Ik) to be used for communication with the UE 201.
With the use of the security-related parameters (ciphering algorithm/integrity check algorithm supported by the UE 201 and the like, for example, START) received from the UE 201 in step 211, the security-related parameters (ciphering algorithm/integrity check algorithm supported by the SGSN 204 and the like, for example, Ck and Ik) received from the SGSN 204 in step 231, and the security-related parameters (for example, FRESH) generated directly by the RNC 203, the RNC 203 generates a Message Authentication Code (MAC) and transmits the MAC to the UE 201 in step 232.
Upon receiving the MAC through step 232, the UE 201 calculates an eXpected MAC (XMAC) with the use of the security-related parameters START, Ck, Ik and the like, kept therein, and the security-related parameters (FRESH and the like) received in step 232.
If the calculated XMAC is identical to the MAC received in step 232, the UE 201 authenticates the RNC 203, and sends a SECURITY MODE COMMAND COMPLETE message in step 233. The SECURITY MODE COMMAND COMPLETE message includes the MAC calculated for the SECURITY MODE COMMAND COMPLETE message by the UE 201. Upon receiving the SECURITY MODE COMMAND COMPLETE message, the RNC 203 calculates an XMAC for the SECURITY MODE COMMAND COMPLETE message. If the calculated XMAC is equal to the MAC received in step 233, the RNC 203 authenticates the UE 201, and sends the SECURITY MODE COMMAND COMPLETE message to the SGSN 204 in step 234, informing the successful execution of the security mode command.
A detailed description of the security mode command procedure in steps 231 through 234 is provided in TS 33.102 v630 and TS 25.331 v670 of 3GPP.
If the security procedure is completed through the security mode command of steps 231 to 234, a RAB for SIP data transmission is set up in steps 241 to 245. The SIP data transmission is not possible until the SIP RAB setup procedure is completed.
Thereafter, in step 251, the UE 201 sends the INVITE, which is SIP data, to the SGSN 204.
In order to allow the UE to receive the existing IMS service operating as described above, SIP data should be transmitted for session initialization of the service.
However, as shown in FIG. 2, in the existing 3GPP system, the SIP data (for example, INVITE) cannot be transmitted until the RRC connection establishment of step 211, the transmission of the service request message of step 221, the security procedure of steps 231 to 234, and the SIP RAB setup of steps 241 to 245 are completed.
As a result, the existing mobile communication system may experience a transmission delay due to service transmission between an end and another end as it supports the IMS service. That is, an end-to-end delay may increase between a destination UE and a source UE, between a source UE and a destination UE, and between a UE and each node.